Al2O3/TiO2 stack layers for effective surface passivation of crystalline silicon

For silicon surface passivation, we investigate stack layers consisting of a thin Al₂O₃ layer and a TiO₂capping layer deposited by means of thermal atomic layer deposition (ALD). In this work, we studied the influence of different thermal post-deposition treatments and film thickness for the activation of passivating ALD Al₂O₃ single layers and Al₂O₃/TiO₂ stack layers. Our experiments show a substantial improvement of the passivation for the Al₂O₃/TiO₂ stack layers compared to a thin single Al₂O₃ layer. For the stacks, especially with less than 10 nm Al₂O₃, a TiO₂capping layer results in a remarkably lower surface recombination. Effective fixed charge density of Al₂O₃/TiO₂ stack layers increases after TiO₂deposition and O₂ annealing. It is also demonstrated that the enhanced surface passivation can be mainly related to a remarkably low interface defect density of 1.1 × 10¹⁰ eV¯¹ cm¯², whereas post-TiO₂ heat treatment in O₂ ambience is not beneficial for the passivation of silicon, which is attributed to increasing interface defect density of stack layers.This project has been supported by the Australian Government through the Australian Solar Institute, part of the Clean Energy Initiative